Since the invention of the integrated circuit (IC), the semiconductor industry has experienced continued rapid growth due to continuous improvements in the integration density of various electronic components (i.e., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from repeated reductions in minimum feature size, which allows more components to be integrated into a given area.
Inductors are essential devices in many integrated circuits, such as radio-frequency (RF) circuits. It is often required that the inductors have high inductance values. This requirement, however, is difficult to achieve on integrated circuits because high inductance needs to be achieved with the cost of high chip area usage.
Particularly in radio frequency (RF) and mixed signal designs, inductors and transformers are commonly used. To improve the inductance of inductors, three-dimensional inductors were developed, wherein an inductor may be formed in a plurality of metal layers to form a helical shape, and the portions of the inductors in different metal layers are interconnected. The further improvement of the inductors, however, is still limited, for example, due to the increasingly smaller distances between metal layers and the respective semiconductor substrate, the requirement for forming dummy patterns, and the undesirable Eddy currents in the semiconductor substrate.